New Types of Ge₂ and Ge₄ Assemblies Stabilized by a Carbanionic Dicarborandiyl-Silylene Ligand

Abstract

The first Ge(0)–Ge­(II) germylone–germylene-paired Ge2 complex (LSi)2Ge2 (4) and the molecular Ge4 cluster (LSi)2Ge4 (5) supported by the chelating carbanionic ortho-C,C′-dicarborandiyl-silylene ligand LSi [L = C,C′-C2B10H10, Si = PhC­(tBuN)2Si] have been synthesized and isolated via reduction of the corresponding precursors chlorogermyl-germyliumylidene chloride (2), [(LSi)2Ge­(Cl)­Ge]+Cl–, and (LSi)2Ge4Cl4 (3) with C8K, respectively. The latter precursors were obtained from the unexpected outcome of the reaction of the ortho-C,C′-dicarborandiyl phosphine-silylene ligand PLSi (1) {P = P­[N­(tBu)­CH2]2} and GeCl2·dioxane. Compound 2 is formed in higher yields (65% yields) by the salt metathesis reaction of the C-lithium dicarborandiyl-C′-silylene salt LiLSi (6) [Li = Li­(OEt2)2] with GeCl2·dioxane. The molecular structures of all these species (1–6) have been established and confirmed spectroscopically and crystallographically. The electronic structures of 4 and 5 were elucidated by density functional theory calculations. While 4 possesses a localized dative Ge(0)→Ge­(II) bond, the Ge–Ge σ bonds in 5 are delocalized in the Ge4 cluster core. Featuring a donor–acceptor interaction between two chelating silylenes and the Ge4 core, compound 5 represents a unique molecular model for a Ge4 cluster.

Distinctly different reactivity of bis(silylenyl)-versus phosphanyl-silylenyl-substituted o-dicarborane towards O2, N2O and CO2

“…Indeed, under the same reaction conditions, exposure of 3 to dioxygen gas at -20 °C resulted in the formation of the CB-Si(=O)P(=O) silanone- 25 shifted relative to that of the precursor 3 (δ = 102.9 ppm). 22 A similar up-field shift is observed for the 29 Si{ 1 H} NMR resonance of 4 (δ = -52.8 vs. 17.5 ppm for 3). 22 The IR spectrum of 4 shows a very strong stretching vibration mode at  = 1193 cm -1 for the Si=O bond, which is slightly larger than the value observed for the Si=O 30 bond in a C=O-supported silanone (1153 cm -1 ).…”

“…22 A similar up-field shift is observed for the 29 Si{ 1 H} NMR resonance of 4 (δ = -52.8 vs. 17.5 ppm for 3). 22 The IR spectrum of 4 shows a very strong stretching vibration mode at  = 1193 cm -1 for the Si=O bond, which is slightly larger than the value observed for the Si=O 30 bond in a C=O-supported silanone (1153 cm -1 ). 27 A single-crystal X-ray diffraction analysis confirmed the presence of Si=O and P=O bonds in 4 with a O1-Si1-P1-O2 torsion angle of 36.8° (Figure 2).…”

“…The four-coordinate Si atom in 5 shows a resonance at δ = -51.9 ppm in the 29 Si{ 1 H} NMR spectrum (measured at -30 o C in d 8 -THF), matching well with that for 4 (δ = -52.8 ppm). In contrast, the marginally different chemical shift at δ = 10 114.2 ppm in the 31 P{ 1 H} NMR spectrum of 5 (vs. δ = 102.9 ppm of its precursor 3) 22 confirms the presence of the unchanged phosphine moiety.…”

“…19 More recently we succeeded in the synthesis of the isolobal phosphanyl-silylenylfunctionalised o-dicarborane CB-SiP (3) where one silylenyl group in 1 is replaced by a phosphanyl moiety. 22 Compound 3 enabled 55 the formation of new classes of C,C'-dicarborandiyl-silylene supported Ge 2 and Ge 4 species which could not be realised with 1. 22 23 As expected, the five-coordinate 29 Si nuclei exhibit a drastic up-field shift in the 29 Si{ 1 H} NMR spectrum (δ = -98.6 ppm) when compared with the precursor 1 (δ = 18.9 ppm).…”

“…22 Compound 3 enabled 55 the formation of new classes of C,C'-dicarborandiyl-silylene supported Ge 2 and Ge 4 species which could not be realised with 1. 22 23 As expected, the five-coordinate 29 Si nuclei exhibit a drastic up-field shift in the 29 Si{ 1 H} NMR spectrum (δ = -98.6 ppm) when compared with the precursor 1 (δ = 18.9 ppm). 19 75 Scheme The reaction of dioxygen with various stable silylenes to afford respective 1,3,2,4-disiladioxetanes is not unexpected and welldocumented.…”